Such a pressure intensifier is known from European patent EP 0 825 348 B1 and from the associated German priority patent DE 196 33 258. In the assembly known from these patents, the working chamber on the low-pressure side of the booster piston is charged and discharged by means of a control piston reciprocated between two positions, a charging position in which it feeds the low-pressure working chamber with low-pressure fluid, and a corresponding discharge position.
However, the known pressure intensifier employs a control piston designed as a one-piece valve actuator. The valve actuator has some special constructional features in order to meet the stated objective of this assembly. According to said patents, the tendency of the valve actuator to vibrate at high frequencies is to be reduced and resonance to be avoided, that is, even at high working frequencies, the valve actuator is supposed to be propelled beyond the mouth of the cylinder line leading towards the low-pressure working chamber of the booster piston as quickly as possible and without being affected by possible impacts, from its charging position in which it connects the cylinder line with the low-pressure feed line, into its discharging position, where it connects the cylinder line with the pressureless tank line. This is supposed to reduce the time the valve actuator requires for a complete and clean reversal from the charging position into the discharging position (and vice versa). The aim is that at high working frequencies, the pressure intensifier piston need not wait unnecessarily long for the valve actuator to have reversed cleanly, and that the entire flow cross section of the valve is then available for charging or discharging the low-pressure working chamber.
Of course, this is a matter of milliseconds for each working cycle that can be gained or lost. However, even small gains in time at each working cycle add considerably if the pressure intensifier is operated at a high working frequency in order to deliver as large an amount as possible of oil under high pressure; the pressure intensifier known from said patents, according to their statements, achieves a respectable delivered quantity at the high-pressure side, i.e. more than 2.5 l/min at a working frequency of more than 30 Hz and a maximum supplied quantity of more than 10 l/min.
In order to achieve such a performance, this known assembly concerns itself with the design of the valve actuator.
One of the two complementary measures that are supposed to increase the oscillation frequency of the valve actuator is that the control line pressure is applied to the valve actuator on its one side and a constant pressure on its other side, that is, the pressure from the low-pressure supply line which is available as the maximum operating pressure. Thus, a constantly maximal force acts on this side. In the reversal phase, this forces the valve actuator to accelerate maximally. The shot from the charging position into the discharging position thus requires as little time as possible. As another indispensable measure, said patents additionally provide a special embodiment of the valve actuator designed as a slide valve. Because the valve actuator is supposed to be configured such that the control disk, whose circumference seals against the cylinder bore, need only be shot from the one side of the mouth of the cylinder line to the other side of the mouth of the cylinder line in order now to connect the cylinder line, instead of with the low-pressure feed line, with the pressureless tank line and vice versa. This control disk forms the actual slide valve, which is unaffected by impacts even at high piston speeds, operates in a short-stroke manner, and has very little mass. The two measures supplement each other.
This design of the valve actuator as a slide gate valve, which as such is rather advantageous, however has certain serious drawbacks. Fundamentally, the manufacture of a slide gate valve is exceptionally expensive. Because the control disk, which in such a valve actuator seals the two sections of the annular space with respect to each other and the cylinder wall, must travel in the cylinder bore it is assigned to at the lowest tolerance. This means that not only must the control disk be ground, but the cylinder bore must be honed above all. Such a honing of the cylinder bore is exceptionally expensive.
Also, such an assembly is very susceptible to wear. Because travel of the control disk must be maintained at the lowest tolerance over the entire life of the pressure booster. This is critical especially if the valve actuator is to travel at extremely high frequencies, thus covering extreme sliding distances during the course of its life. At the high frequencies intended here, small dirt particles having an abrasive effect already suffice to generate scores and the like in the control disk and/or the cylinder bore, thus reducing the quality of the sealing effect of the slide gate valve or disabling its sealing function to the point of unserviceability.
In addition, repair of such a slide gate valve is very complex. The cylinder bore must be rehoned for the repairs (as a rule, the alternative, possible use of a new casing is uneconomical because in most cases, the slide gate valve is accommodated together with the booster piston in a joint casing). It thus becomes oversized, i.e. its diameter becomes larger. Therefore, no series-produced slide gate valve can be inserted into the rehoned cylinder bore anymore. Instead, a slide gate valve has to be inserted which is produced as a special spare part, with the slide gate valve being correspondingly oversized at its outer circumference. This requires elaborate storage and the costly manufacture of special components.
The pressure boosters of the type addressed herein, as a matter of principle, can be fed with different amounts of pressure, therefore supplying high pressures without any reconfigurations or adjustments being necessary. Since such pressure booster are very often used in a mobile manner, for example on construction sites, this is a great advantage; to a large extent, a pressure booster makes do with the available feeding pressure. With regard to the pressure booster proposed in the patents mentioned in the introduction, which is actually being built, it is known that it is suitable for being fed with pressures from about 35 to about 300 bar. Given a pressure boosting ratio of, for example, 4:1, about 140 to 1200 bar are thus available on the high-pressure side. A feed at higher pressures, such as 350 bar, 500 bar or more, poses problems in this pressure booster due to the leakage flows which then occur to a very considerable extent at the control disk, unless a very expensive control disk with an extremely exact fit is used in a special case, which could possibly push the limit up slightly. If only higher feeding pressures are available (e.g., during mobile use), they must be reduced prior to being fed into the pressure booster, which is uneconomical.
In view of this, it is the object of the invention to avoid these drawbacks.